The PCB layer is divided into signal layer, internal power layer, screen printing layer, mechanical layer and shielding layer. Now let's introduce the definition of PCB layers
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Signal layer
Signal layers include top layer, bottom layer and mid layer
The top signal layer is also called component layer. Its main purpose is to place components, but for double-layer PCB board and multi-layer PCB board, it can be used to lay wires or copper
The bottom signal layer is also called welding layer, which is mainly used for wiring and welding, but for double-layer PCB board and multi-layer PCB board, it is the place where components can be placed
The middle layer is usually used for laying signal lines (excluding power lines and ground wires) in multi-layer boards, with a maximum of 30 layers
The top layer, bottom layer and middle layer can be connected by via, blind via and buried via
Internal power layer
The internal power layer is the internal electric layer. The number of PCB layers is the sum of the signal layer and the internal electric layer. The inner electric layer and the inner electric layer, and the inner electric layer and the signal layer can also be connected with each other through through holes, blind holes and buried holes, just like the signal layer
Screen printing layer
The purpose of the screen printing layer is to place the outline and label of some components, various annotation characters and other printing information, so as to facilitate the later welding of components and circuit inspection. The silk screen layer is usually white. A circuit board can have two silk screen layers, which are top overlay and bottom overlay
The top screen printing layer is mainly used to mark the projection outline, label, nominal value or model of components and various annotation characters
The function of the bottom silk screen layer is the same as that of the top silk screen layer. If the top silk screen layer can contain all the label information, the bottom silk screen layer can be closed
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Mechanical layer
Mechanical layers are generally used to place indicative information about PCB manufacturing and assembly methods, such as PCB dimensions, dimension marks, data, via information, assembly instructions, etc
Shielding layer
Altium designer provides two mask layers with both top and bottom layers: solder mask and paste mask
Assembly layer refers to the green part of PCB board, because it is negative output, so the effect of solder mask is not solder mask, but silver tin
The solder paste layer is used for machine placement, which corresponds to the pads of all the placement components. The size of the solder paste layer is the same as that of the top layer / bottom layer. It is used to open the tin leakage of the steel mesh
The paste absorbing layer is only used in machine placement. It corresponds to the pad of all the placement components, and is the same size as the top layer / bottom layer layer, which is used to open the tin leakage of the steel mesh.
